What is the Electrical Power Calculator?
This calculator finds the real power (in watts and kilowatts) delivered by an AC electrical circuit from the measured voltage, current and power factor. It supports both single-phase circuits (typical household supplies) and balanced three-phase circuits (common in industrial and commercial installations).
How to use it
Select whether your circuit is single-phase or three-phase. Enter the voltage in volts (for three-phase use the line-to-line voltage), the current in amperes, and the power factor (a number between 0 and 1, where 1 is a purely resistive load). The calculator instantly returns the real power in kilowatts and in watts.
The formula explained
For a single-phase circuit, real power is $$P = V \times I \times \text{PF}.$$ For a balanced three-phase circuit using line-to-line voltage, an extra factor of \(\sqrt{3}\) (about 1.732) is applied: $$P = \sqrt{3} \times V \times I \times \text{PF}.$$ Dividing by 1000 converts watts to kilowatts. Power factor accounts for the phase shift between voltage and current; reactive loads such as motors have a PF below 1.
Worked example
A three-phase motor draws 20 A at 400 V with a power factor of 0.85. Real power $$= \sqrt{3} \times 400 \times 20 \times 0.85 = 1.732 \times 6800 = 11{,}778 \text{ W} \approx 11.78 \text{ kW}.$$
FAQ
What voltage do I enter for three phase? Use the line-to-line voltage (e.g. 400 V or 415 V). The \(\sqrt{3}\) factor already accounts for the conversion.
What if I don't know the power factor? A resistive load (heaters, incandescent lights) is close to 1.0. Motors are typically 0.8–0.9. If unknown, 0.9 is a reasonable estimate.
Does this give real or apparent power? Including power factor gives real (active) power in kW. Set power factor to 1 to get apparent power in kVA.
